Asp.net web api 未为飞行前CORS请求调用WebApi DelegatingHandler

我正在尝试为我的WebApi控制器实现CORS支持，下面就是一个例子

我的处理程序如下所示：

/// <summary>
/// Taken from http://blogs.msdn.com/b/carlosfigueira/archive/2012/02/20/implementing-cors-support-in-asp-net-web-apis.aspx
/// </summary>
public class CorsHandler : DelegatingHandler
{
    private const string Origin = "Origin";
    private const string AccessControlRequestMethod = "Access-Control-Request-Method";
    private const string AccessControlRequestHeaders = "Access-Control-Request-Headers";
    private const string AccessControlAllowOrigin = "Access-Control-Allow-Origin";
    private const string AccessControlAllowMethods = "Access-Control-Allow-Methods";
    private const string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
    private const string AccessControlAllowCredentials = "Access-Control-Allow-Credentials";

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var isCorsRequest = request.Headers.Contains(Origin);
        var isPreflightRequest = request.Method == HttpMethod.Options;
        if (isCorsRequest)
        {
            if (isPreflightRequest)
            {
                var response = new HttpResponseMessage(HttpStatusCode.OK);
                response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());

                var accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault();
                if (accessControlRequestMethod != null)
                {
                    response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod);
                }

                var requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders));
                if (!string.IsNullOrEmpty(requestedHeaders))
                {
                    response.Headers.Add(AccessControlAllowHeaders, requestedHeaders);
                }
                response.Headers.Add(AccessControlAllowCredentials, "true");

                var tcs = new TaskCompletionSource<HttpResponseMessage>();
                tcs.SetResult(response);
                return response;
            }

            var resp = await base.SendAsync(request, cancellationToken);
            resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());
            resp.Headers.Add(AccessControlAllowHeaders, "*");
            resp.Headers.Add(AccessControlAllowCredentials, "true");
            return resp;
        }
        return await base.SendAsync(request, cancellationToken);
    }
}

Request OPTIONS /api/campaigns/1002/customerusers/1008 HTTP/1.1
Accept  */*
Origin  http://app.dev.alanta.com
Access-Control-Request-Method   DELETE
Access-Control-Request-Headers  accept
Accept-Encoding gzip, deflate
User-Agent  Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)
Host    dev.payboard.com
Content-Length  0
DNT 1
Connection  Keep-Alive
Cache-Control   no-cache

它被要求“获取”请求。但它没有接到任何需要飞行前批准的请求。请求如下所示：

/// <summary>
/// Taken from http://blogs.msdn.com/b/carlosfigueira/archive/2012/02/20/implementing-cors-support-in-asp-net-web-apis.aspx
/// </summary>
public class CorsHandler : DelegatingHandler
{
    private const string Origin = "Origin";
    private const string AccessControlRequestMethod = "Access-Control-Request-Method";
    private const string AccessControlRequestHeaders = "Access-Control-Request-Headers";
    private const string AccessControlAllowOrigin = "Access-Control-Allow-Origin";
    private const string AccessControlAllowMethods = "Access-Control-Allow-Methods";
    private const string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
    private const string AccessControlAllowCredentials = "Access-Control-Allow-Credentials";

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var isCorsRequest = request.Headers.Contains(Origin);
        var isPreflightRequest = request.Method == HttpMethod.Options;
        if (isCorsRequest)
        {
            if (isPreflightRequest)
            {
                var response = new HttpResponseMessage(HttpStatusCode.OK);
                response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());

                var accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault();
                if (accessControlRequestMethod != null)
                {
                    response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod);
                }

                var requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders));
                if (!string.IsNullOrEmpty(requestedHeaders))
                {
                    response.Headers.Add(AccessControlAllowHeaders, requestedHeaders);
                }
                response.Headers.Add(AccessControlAllowCredentials, "true");

                var tcs = new TaskCompletionSource<HttpResponseMessage>();
                tcs.SetResult(response);
                return response;
            }

            var resp = await base.SendAsync(request, cancellationToken);
            resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());
            resp.Headers.Add(AccessControlAllowHeaders, "*");
            resp.Headers.Add(AccessControlAllowCredentials, "true");
            return resp;
        }
        return await base.SendAsync(request, cancellationToken);
    }
}

Request OPTIONS /api/campaigns/1002/customerusers/1008 HTTP/1.1
Accept  */*
Origin  http://app.dev.alanta.com
Access-Control-Request-Method   DELETE
Access-Control-Request-Headers  accept
Accept-Encoding gzip, deflate
User-Agent  Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)
Host    dev.payboard.com
Content-Length  0
DNT 1
Connection  Keep-Alive
Cache-Control   no-cache

但正如我所说，处理程序从未被调用选项动词

我原以为可能有其他处理者在某处干预此事，但我已经排除了所有可能的候选人，到目前为止没有运气

我的另一个理论是，它没有识别选项动词的特定路径，因此它从不将请求传递给WebApi子系统，而是在其他地方处理。但我不完全清楚如何解决这个问题

---

建议？

将以下内容添加到web.config：

<handlers>
    <remove name="OPTIONSVerbHandler" />
</handlers>

CORS如何？我对此进行了研究，但（在我的简短探索中）我看到的主要问题是，我需要能够在运行时动态指定“访问控制允许源”，因为将其设置为“*”会阻止您使用“访问控制允许验证”头。也许它有办法做到这一点，但我没有发现。尝试将此添加到web.config:

就是这样！具体来说，OPTIONSVerbHandler。把它放在一个答案里，我就相信你了。谢谢<代码>返回响应？IMHO应

返回tcs.Task